header photo is very blurry!

i uploaded a photo for the header on my blog and it is so blurry!! I cannot figure out why this is happening and I really do not like the way it makes the cover page look! the photo is so big, which is another thing....is there a way to make it smaller? I would love your assistance in the look of my page. thanks!
Blog url: http://fitwithcybill.wordpress.com/